With increase in the speed of information transmission of communication devices in recent years, signal transmission using light have been replacing conventional transmission using electrical signals and prevailing widely. Information communication devices using light are adapted to convert an electrical signal into light using a transducer such as a light emitting element, transmit the light to a light receiving element, which is another transducer, through an optical waveguide, and convert the light into an electrical signal again by the light receiving element. The optical waveguide is composed of what is called a core, which mainly transmits light, and what is called a cladding, which surrounds the core.
Actually, according to a method of manufacturing a communication device for optical signals, a light emitting element such as a laser diode is set at a fixed location in such a way as to emit light to the central portion of the core in the direction in which the core extends, and the light receiving element such as a photo diode is set at a fixed position in such a way as to receive light exiting from the central portion of the core in the direction in which the core extends, perpendicularly by its central portion (see patent literature 1). In this case, the accuracy of positioning of the light emitting element and the light receiving element relative respectively to the light entering the core and the light exiting from the core directly affects the intensity of the light signal. Therefore, when the light emitting element and the light receiving element are mounted on a substrate provided with an optical waveguide, the accuracy of mounting is important. In most cases, a reflecting mirror that changes the direction of light is provided between the optical waveguide and the light emitting or receiving element, and what actually matters is the alignment of the reflecting mirror and the light emitting or receiving element. Patent literatures 1 or 2 and 3 disclose methods of preferably aligning the light emitting or receiving element and the optical waveguide.